[TYPO3-doc] Mentioning Github in Feedback section of each manual

[François Suter]

Hi Michael,

> +1 ... sounds good to me :-)

Thanks for the feedback. I'll proceed, since I have planned the time for 
it today.

Cheers

-- 

Francois Suter

Work: Cobweb Development Sarl - http://www.cobweb.ch

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